Line switching systems



March 8, 1960 B. BLAKELY, JR

' LINE: swITcHING SYSTEMS March 8, 1960 B. BLAKELY, JR

LINE swITcHING SYSTEMS 4 Sheets-Sheet 2 Filed April 22, 1958 km, .wsu

N GP* A TTORNE Y March 8, 1960 B. BLAKELY, JR

LINE swITcHING SYSTEMS 4 Sheets-Sheet 5 Filed April 22, 1958 A, T TORNEY B. BLAKELY, JR

LINE SWITCI-IING SYSTEMS March 8, 1960 Filed April 22, 1958 4Sheets-Sheet 4 @SMQ A TTORNE V 2,927,968 LINE swrrcHiNG SYSTEMS BryceBlakely, Jr., Murray Hill, NJ.,

' Telephone Laboratories, Incorporated,

N. a corporation of New-York Appneation April zz, 195s, serial No.730,088 7 claims. (ci. 179-15) assiguor to Bell New York,

This invention rela-tes to multi-channel communication systems and, moreparticularly, ,to line switching circuits `for use with such systems. r

In communication. systems employing long and expensive transmissionfacilities, such as trans-oceanic submarine cable facilities, it iseconomical to utilized terminal facilities which insure .full -use vofall of ,the availlable channel time. One system proposed` for saving`channel time is based on the statistical fact that conversations usethe facilities, on the average, for less than lone- Athird of the time.Therefore, by interconnecting vthe two parties only when the line isactive, large savings in channel time `may .be effected. The terminalfacilities which perform this function have xbeen xtermed ftirne'assignment speech interpolation systemsor, more conveniently, TASIsystems. One such system is 'disclosed Ain the copending applicationofF. vA. Saal and I. Welber, Serial No. 686,468, tiled September 26, 1957.

.By utilizing TASI facilities vat the terminals of the :transmissionsystem, .the capacity, in total number v of \conversations carried, .o fthe system can be doubled or even tripledl by assigningthe transmissionchannels of the system to the talkers being served only whiletheyareactually active, i.e speaking, In ,order tosecure Ithe .benefits ofspeech interpolation, hoWYcl', a rather `com- .'plex switching-arrangement is required at each end of lthe transmission system Itoperform the necessary con- :nections and ,disconnectionsl Theseswitching arrange- :ments include, in addition .to individualtalker-to-channel switches, a large amount of common control equipment.to supervise and monitor the .operation of lthe switches. .Any failure,however small, in this common control `equipment could result in thefailure of the entireftime .assignment speech interpolation facilitiesand thus ter- `minate the use of the transmission system entirely. Itshould be observed, however, that vin such an event, the transmissionmedium might itself be completely opera- .tionaL It is an object of thepresent invention to insurethe `utilization of transmission systemsincorporating time as- ;'signment speech interpolation facilities to.their ,fullest f'capacity.

4It' is another object of the present invention to switch #timeassignment speech interpolation facilities into and :fout of service in-a communications system.

It is a more specific object of the inventionV to main stainsubstantially continuous service to selected custom- ,ers using acommunication system incorporating time assignment speech interpolationyfacilities uponfailure of :those facilities.

It is yet another object of the invention to switch time :assignmentspeech interpolation facilities at each end of ,a long transmissionsystem substantially simultaneously.

In accordance with the present invention, the above lobjects areachieved in a communication' system by removing TASI facilities fromservice and simultaneously connecting the channels of the transmissionsystem to an equal number of the customer lines-previously being;`

2,927,968 Patented 8, 196@ served by the VTASI facilities-1, By the useo f automate cally/.responsive devices and by means of coded signalstransmitted between terminals, the switching of the TASI facilities canbe made suciently smooth to provide substantially uninterrupted serviceto the customers switched directly to the transmission channels.

More specifically, a TASI terminalat one end of the transmission systemin which a failureoceurs initiates a switching signal which istransmitted, via the transmission system, tothe remote terminalk at theother end.

The remote terminal then returns a verification signal to the initiatingterminal to cause actual switching. The remote terminal itself is madeto `wait .a .period of time equal to thepropagation time of thetransmission system .before switching. The two terminals' thereforeswitch 'simultaneously' and' provide continuous through service. Afeature of the present invention resides in the use `ofthe sameequipment for emergency switching as is used for removing and replacingthe TASI facilities for routine purposes,. such as periodic maintenancetests and intimes of low traffic volume. I

Another feature-of the present invention resides in the use of the sameswitching facilities to remove individual transmission channels from theTASI facilities and thus allow their use for full-time transmission, forexample,

for program service. v

' These and other objects and features, the nature of the presentinvention and lits various advantages, will be morel fully understoodupon considerationof ythe ,accompanying drawings and v,of the followingdetailed description of the drawings. Y a

In the drawings:

Fig. 1 is `a simplified functional block diagram of a Ycommunicationsystem illustrating the switching arrangements of thepres'ent invention;

Figs. 2 through 4, when arranged in the manner shown in Fig. 5, comprisea detailed block diagram of one terminalstationof a time assignmentspeech interpolation switching system embodying the .principles ofthe 'vpresent invention; and v Fig. 6 is a block diagram of a complete systememploying two terminalstations' such as those illustrated in Figs. '2through 4 connectedr by tivoA separate one-way.

transmission media.

Referring more particularly to Fig. 1, there is shown a lfunctionalblock diagram of a line switching arrangement whichc'an'be used inconjunction 'with time assignment speech interpolation facilities in acommunication system. An essential part of the communication systemillustrated is a'transmission medium 1 0" which may be a carriertransmission line or any other multi-channel transmission facility.lTransmission medium 10 is' illustiated in Fig. l as a coaxial cablewhich is capable, by means of frequency multiplexing techniques, ofcarrying a Xed number c of individual communication channels. Thus, amodulator -11 converts signal waves on its c input terminals toa singlefrequency multiplexeclsignal on its .l output terminal.l Similarly, ademodulator 12 recouvertsY the frequency multiplexed signal ontransmission medium 10 to individual signal waves on c output terminals.

In order tomorefully utilize the capacity of the transmission channelsprovided by transmission facility comprising modulator 11, transmissionmedium '1Q and demodulator 12, Ytime assignment speech interpolation(TASI) transmitter. 13 assigns n talker lines tothese e transmissionchannelslfonly while the individual talker l lines are active, that is,are actually carrying speech signal Waves. Since n may be much greaterthan c, asgnicnt increase` in transmission .efficiency is achieved,ljasmeasured by vthe, number of individual talkers accommodated by the Same@transmission channels. A TASI receiver' 14 at the remote end of thetransmission facility 160 assigns the other ends of the c transmissionchannels tothe appropriate ones of n listener lines to complete aconnection from an individual talker to the proper individual listener.Time assignment speech interpolation facilities forperforming thesefunctions are disclosedein detail in theV aforementioned copendingapplication of F. A. Saal and I. Welber.

In accordance with the present invention, means are provided to bypassthe time assignment speech interpolation facilities and connect c of thetalker lines and listener lines directly to the c transmission channelsaorded by transmission facilityv 160. Primary line switch 15 is providedto perform this function. The switchingarrangements for only one of thec lines isv illustrated since the'facilities Vfor the remainder of thelinesl -are merely duplications of the one illustrated. t y

Thus, c"A of the n talker lines are, fof convenience,

termedprimary lines and are introducedintop'primary `lineV switch 15. Arelay 16 is provided to connect talker line 1 directly to transmissionchannel A or,y alternatively, through 'tASl4 transmitter 13 to any oneof the c transmission channels. Thus, contacts 1'/ and v18 wil'lconnectprimary line l directly 'to transmission channel A. Contacts 19 and 20,*on the other hand, `connect primary line 1 to the input of TASItransmitter 13 and connect transmission channel A to the output of TASItransmitter 13, A simple and ecient means yis thus provided forinserting or removing the TASI transmitter 13 from service.

Relay 16 has two windings, one of Vwhich is energized by ,arvoltage onlead 21 and the other of which is energized by voltage on lead 22. Lead21 is connected not only to relay 16 but also to all of the relays forthe remainder of `thee primary lines. Lead22, on the other hand, isconnected to a switch 23 which serves to connect a battery 24 to thislead and thus to energize it on an individual basis. An individual lineswitch similar to switch 23 is provided for each'ofthe relays asociatedwith the c primary lines. A voltage on lead 21 serves to connect all ofthe c primary lines directly to the transmission channels while avoltage on'lead 22 serves to connect only primary line 1 directlytotransmission line A.

` At the receiving terminal, primary line, switch `25 is provided with arelay 26, an individual line switch 27 and a common control lead 28which perform corresponding functions `at the yreceiving terminal.`Itjshould be noted that, although the line switches are illustrated aselectro- Lll) mechanicalswitches, any equivalent electronic switchingcircuit would be equally suitable, particularly where rapid switching isdesired. An electronic switch suitable for this purpose is disclosedinthefcopending ,application of I. D. Iolrannesem l?. B. Myers and .lSch-wenken Serial No. :570;53G`flled March '9,l '1956s.

Returning to'the transmission terminal, it can be seen that o'fthentalker lines being served by lthe TAS facilities, n-c lines remain asinputs to TASI transmitter 13.

An excess line switchV 29 is provided 'to disconnect these rvz--c excesslines vfromthe input of TASI transmitter 13. Excessline switch 29comprises a plurality ,of'relays ,such as relay 31to perform thisoperation foreach of theexcess lines. Similar relays, notillustrated,are provided, one for lrecorded.message sonrce 36.- ',As vthetransmission terminal, eac-h .of the excess ,-lines is ,provided with asimilar relay and set .of contacts. All, of these relays are operatedby'a .voltageon aV commoncontrol lead 37.

assignee .Y (Y

ceiving terminal are controlled by a signal and control Vcircuit 39. Thefunction of these signal and control circuits 38 Yand 39 will be morefully described hereinafter, but it can be stated here that theswitching operations at the transmission and receiving terminals arecaused to take place substantially simultaneously and automatically inresponse to a failure of the TASI facilities by means of control signalstransmitted over signaling channels 40 and 50. s v

lt can be that the switching system of the present invention serves topreserve the basic capacity of transmission facility'ltl by insuring theuse of these facilities after a failure in the'TApSI facilities 13 or14. This is accomplished by maintaining a connection between at least cof the n talker lines and the corresponding c listener lines duringsucha failure.

At the receiving terminal, the excess lines are connected to a recordedmessage source 36 at the time the TASI facilities are yretrieved f rernservice. The function' of recordedrmessage source 36 is tio apprise theylisteners connected to the excess lines that they are no longer beingservedand to instruct Vthem how to proceed toisecure a In Figs. y2through 4, when yarranged Aas shown in Pig. 5, y

there is shown a detailed block diagram of one terminal station of aline switching system in Aaccordance with the present invention. inFigs. 2 through 4,v components which are the same as the components ofFig. l are identitied by the same reference numerals. Thus :in Fig. y2the transmitting inpnt lines to a time assignment speech interpolationtransmitter L3 are divided into primaryV lines and excess lines. Theprimary lines are lconnected by way of primary line switch 15 to `therinput of the TASI transmitter i3 and then tothe vinput of modulator 110r, alternativelygdirectly to the input of Imodulator 11. The excesslines are connected by way of excess `line Iswitch 29 to the vinput toTASl transmitter '13.

Similarly, in Fig. y4, primary -line switch 25 connects the output-s ofdemodulator k12 to the input of TASl receiver 14 andthen tothe receivinglines or, alternatively, directly to the receiving lines. =Excesslineswitch -33 likewiseconnectsthe balance of the receiving lines to theoutput of `TASI receiver 14. Y i n 'It will be noted'thatFhigsf-Zthrough 4 illustrate only one'terrninal station of acomplete/communication system utilizingvthe-switohing arrangements ofthe present jinvention. Thus-the receiving equipment illustrated fFig 4is @muy at the Same ssii f .transmisin faaility as is "the transmittingequipment illustrated in ,Fig.`2. It is to be understood, however, thatthe' invention contemplates'a duplication of the .entire terminalstation illustrated in Figs. 2 through A4.at thezremote end oftransmission lfacility 16010 .form a fully symmetrical switching system.Such an arrangement has lbeen Villustt-ated inblock form in Fig. 6. :Forconvenience, however, only v`one terminal stationhas been illustrated indetail. This presentation has beeinfonnd `to be desirable due to thefact that the present inventioncontemplates a complete round trip Yofcontrol signals and.hence requires local receiving as Well astransmission facilities. When describing the operation V,of the`switching-system, Vfunctions to be carried on at the remote terminalstation will Ybe'describedwitl'ireferfence to-the local terminal stationwith which it -is identical.

Proceeding now to a detailed description of the func-V A tionalblock'diagramV ofFigs.V Zithrough 4, it will bel seen 4The primary andexcess line, switches4 at the transmission terminal'are controlledrbyasigr'lal and control circuit 38 while thev primary. and,excessliliersvvitcrhesk at therethat Figs. 21and4 correspondwroughly to`theswitching portions,of'thefsirnplied,block diagram of Eig. 1. jFig. 3,sa theage, hanrofrssrssds. t0 .the Signal and. @11u01 j switch-out cannow be made.

circuit'38 or 39 inA Fig. 1. The description'of the detailed blockdiagram will be begun with Fig. 3.

' If, as is proposed by the present invention, it is desired to switch aplurality of communication links while they seconds might be interpretedby -the human ear asan interruption in service. Interruptions of lesserduration are imperceptible or are interpreted as hits,-.i.e.,interference. VIt is therefore desirable that a switching system whichsubstitutes direct connections for connections through ATASI equipmentwill complete the direct connections within 150 milliseconds oftheactual failure.

Even more important, however, particularly in. the case of partialfailures of the TASI equipment, is that the local and the remoteswitching operations be substantially simultaneous, i.e., within a fewmilliseconds of each other. This isy true because any customer whocontinues to receive service through partially impaired TASI equipmentis much more sensitive to two-separate switching opera'- The of meetingboth of these standards, even on exceptionally long transmissionfacilities such as trans-oceanic submarine cables..

64 in their components. This is trueqbecau'se substantially the sameprocedure is used for switch-in as is used vfor switch-out. lTheswitch-out logic Vcircuit 101 will be described in detail and identicalreference numerals with a prime will be usedV to designate thecorresponding components of thev switch-in logic circuit 100.

Upon the occurrence of a complete or partial failure in the TASI controlequipment, a signal condition such as a pulse is introduced on lead 150.This signalin-g condition is, in the vpreferred arrangement, generatedlautomatically upon such a failure by any means known to the art. It mayalso, however, be generated manually by the operation of a switch. Themeans for generating such a signal hasy not beenrillustrated since itforms no part of the present invention and can take any one of manyforms. i

The signaling condition on lead 150 serves to set a bistable device 104,for example abistable multi-vibrator circuit, and thus producean outputon lead 105. vThe output on lead 105 enables OR gate V106, the output ofwhich is used to partially enable AND gate 107. Simultaneously, theoutput on lead 105 is also usedv to enable the four-input OR gate 108.The-.output of OR gate 108 is simultaneously introduced into timing andrepeater circuit 102 and amplier 109. The output of in Fig. 2 and seizesignaling channel 111 from the TASI In general, the system of thepresent invention operates 'i lto fill the above and other requirementsby means of coded switching signals transmitted back and forth betweenthe local and the remote terminal stations. Upon occurrence of afailure, theterminal station in which the failure occurs initiates amultifrequency coded switch-out signal which is transmitted to theremote terminal station.

Upon receipt of this switch-out signal, the remote terminal stationtransmits back afverilication signal indicating that the switch-outsignal hasbeen received and that The remote' terminal station then waitsfor a period of time equal to the propagation time of the transmissionfacility before switching.

The local terminal station switches as soon asfit receives theverification'signal. In this'way both terminals switch simultaneously.Switch-in (replacing 'the" TASI facilities in service) is carried on 'ina similar manner.

Should the switch-outfsignal be lost or obscured by noise, means arealso provided to repeat the switch-out` Furthermore, if no veriicationis received after a reasonableV number of trys, an alarm.

signal at xed intervals.

Proceeding to a detailed description of Fig. 3 of thel equipment for usein transmitting 'switch-out signals.

In' timing and repeater circuit 102, theoutput of OR gate" 108 is shapedto produce asharptpulse by differentiating circuit 112 and utilized toenable OR gate 113. The output o fOR gate 113 serves to set bistabledevice 114 and producej an output on lead 115. vThe A output'on lead 115is' utilized to complete the enablel ment' of AND gate 107 and thusproduce a signal on,

output lead 116. This. signal on lead 116 is introduced into a signalingtransmitter 117 `which then generates the critical. However, amultifrequency tone signal coded in a somewhat complex code pattern,such as a fouroutof-fteen code, is Yparticularly suitable. The morecomplex the coded switch-out signal, the less apt the receivingequipment is to operate erroneously in response to noise or othersignals.

Returning to timing and repeater circuit 102, the output ofdifferentiating circuit 112 is also used to enable drawings, there areshown three major logic units come prising switch-in'logic circuit 100,switchoutlogic -cir'cuitjk v 101 and common ltimer and repeater circuit102. These three logic circuits consist, in part, of #AND and OR gateswhich have been s c'zhematicallyz,representedV in a conventionalnotation.

rTheaAND gates havev thus beenfrepresentedby semi-v l circulary gures'each having a plurality of inputv lines drawn`exactly to the straightline portion of the ligure and a 'single'output'i'line drawn to thecurved portion of the n: wiu be'nofd that switch-in logic circuit 10oana switch-.out logic` circuit 101 are substantially identical OR gate121, the output ofv which is `applied to a timing circuit 122. Timingcircuit'122pr0duces an output on leady 1 23 a ixed time interval, forexample ten milliseconds, afterbeing triggered by the output of 'OR gate121. Timing circuits of this type are well known in the vart and may"comprise, jfor example, a monostable multivibrator with a xed recoverytime. The outputof. timing circuit 1.22 on lead 123 enablesOR gate 124,the output of which resets bistable device 114 and removes the outputfrom lead 115.

It can be seen that timing circuit 122 determines the duration of theswitch-out signal.v This switch-out signal continues for the periodvvduring which an output Yappears onlead 115. This output is initiatedwhen bi stable device 114 is set by the output of OR gate113A v and isterminated ten milliseconds laterwhen'bistabledevice114 is reset by theoutput of OR gate 124. VThe' duration of ten milliseconds wasA chosenbecause tonecoded signals require approximately this duration to beeasily recognizable byreceiving .equipment of economical--k design. Y li The; output of bistable device 114, which appears om lead 115,; isalso `shaped in. diterentiating circuit1119i Y a and applied to a timingcircuit 120. Timing circuit Vv1.20 is similar to timing circuit 1:22Aexcept that its timing period s significantly greater than that oftiming .circuit 122, for example, 100 milliseconds. Therefore, after aperiod of 100 milliseconds, timing circuitt120 produces an output whichfirst sets bistable device 114 through OR gate 113 and then, after adelay of ten milliseconds, resets bistable devicelli throughk OR gate`121, timing circuit 122 and OR gate 124. c flt can be seen that timingcircuit V120 provides 'for a repetition of the switch-out signals atintervalsjof l() milliseconds and would, if not inhibited as later de'scribed, continueY to do so indefinitely. ProvisionV for repetition ofthe svvitchfout signal is made in order to insure that the rerrrcteterminal/receives the. switchen signal even after one of the signals islostby noise d is' tortion or service, interruption.

In order to complete the description of the switch@ outoperation, it isnecessary to show what the remote terrrrirra Vccs with theswitchrcutsignal: Since bett3 terminals are identical, this will befdescribedwithrefl erence to the local terminal illustrated in Figs. 2 through 4.' itshould be remembered, however, that the following operations actuallytake place at the remote terminal.

Proceeding to Fig." 4 of the drawings, the receiving terminal of a TASiswitching system is thereV shown which includes, in part, a signalingVchannel 125, correr spending to the signaling channel 11H1 at thetransmitting terminal. Signaling channel 125 is connected to signal ingreceiver 125 which'is adapted to receive and recognize the signalsgenerated in the remote signalingy trans mitter similar to signalingtransmitter 1177 of Fig. 2.

Upon receipt of the switch-out signal appearing on l signaling channel125, signaling receiver 126 produces an` output on lead 127, indicatingthat such a switch-out signal has been received. Thesignal on lead ,127serves to set bistable device 12Sand produce an output on lead 129. "theoutput kon lead 129 is introduced simultaneously into AND gate 130, ANDgate 131 and dela)l circuit 132. If the circuitry of Fig. 3'is now takenas the remote terminal switching control circuitry, bistable device 104is not set and no output appears on lead Y165. On the contrary,` anoutput appears on lead133, which, together with the signal on lead 129,completely enables AND gate 130 to produce an output which venables OR`gate 106. `In this way the transmission ofa switch-` out signal isinitiated at the remote. terminal. This;

switch-out signal now represents, hofwever, a. verification that theswitch-out signal has been received;y The output of OR gate 106 isintroduced in to AND. gate 167 as before while theA output of AND gatel1,30l is introduced into OR gatel 168 and thence, to the amplifier 109and timing and repeater circuit 102. The operation inV this respect isidentical to that described above when the control circuitry of Fig. 3was assumed to be the local terminal.

The output of bistable device 128 is also introduced into delay circuit132. Delay `circuit 132 delays this signal by an interval of time whichis substantially equal to the propagation time of the transmissionsystem between the local and remote TASI terminals. After such a delay,this signal is applied to enable OR gate 134 and produce an output whichis applied to amplifier 135. rfhe output of amplifier 135 is, in turn,applied to switchout bus 136. f

The signal appearing on switch-out bus 136i is utilized to vperform theprimary and excess line, switching operations at the transmittingterminal, described'in4 detail with reference to Fig. l. Thusein Fig.2,I switch-out bus e 136 isconnected to transmittingupriniary lineswitch 1S and simultaneously to transmittingv excess line switch 29. Attransmitting primary lineY switch 1S it operates to disconnect theprimary lines Vfrom TASI transmitter 13 and connect them directly tomodulator 11. `At transmitting excess.` line switchA 29, however, thesignal on` switch-out InFg- 4 the signal Von switchfout bus 136 isutilized f to perform the corresponding primary and excess lineswitching operations at the receiving terminal, also discussed iiidetailwith reference to Fig. l. Thus switchout bus. 136 is. connected toreceiving primary line switch 25 and srrrultauecuslv tcy receivingexcess line switch 32 and message recorder. 3i6- At. receiving nrirrrsrvline.

s WtchZS itcperstes tc disccnnect theprimary lines from TASI receiver leand. ccrrnect them directly to, demodulatcr l2: At.; receiving, excess.line switch. 33. the signal cu switc -cut bris 136 Operates t0.disconnect the excess lines. rem TASI receiver 1.4 and to. conneetk themto message recorder 36. The primary and excess line switching lrelaysmay also be equipped with holding circuits which are disabled by asignal on switchin bus 137. r

The purpose of the recorded message on recorder 36 is to apprise thelisteners connected to the excess lines that service has beeninterrupted and that alternate connections will be made as soon aspossible. Without such a provision,` these listeners would believe thattheir connectionsV havebeen inadvertently cut off and Vwould signal theoperator for help. Since a large number of them might do so` at once,confusion and slowrservice would result. A carefully formulated recordedmessage acquainting them with a set procedure to follow is thereforedelivered to them to diminish the confusion and speed up service.

' Returning to the control circuitry of Fig. 3,I it can be seen that asignal on lead 150 indicating a failure and calling for switchout causesa switch-out signal to be recurrently transmitted over the signalingchannel. When this switch-out signal is received by the remote terminal,a verification signal having the same form as the switch-out signal isrecurrently transmitted back to the local station.l 'Assuming once morethat the circuits of Figi. 3 comprise the local control circuitry, adescription. cf the Operation ofthe systemv will be con `timied. Y

as,Y at` the remote terminal, is introduced into AND gate Y 131i, ANDYgate 1,31 and'delay circuit 132. Since this terminal initiated theswitch-out operation, however,

there is no output on lead 133 to complete the enablement of AND'gate130. On the contrary, an output exists on lead which output is coupledinto AND gate 131. The enablernentV of AND gatey 131 being thencompleted, an output is produced which is applied simultaneously to ORgate 133 and OR gate 134. The output of OR gateA 134, after beingamplifiedl in amplifier 135,V is applied to theswitcheout bus ,5136 atthe1local terminal to perform all, of the switching operationsldescribedwith reference to the remote terminal. That is, boththe transmitting andreceiving primary and excess.k line switches are operated to remove. theTASI equipment fromy service, connect the primary lines'directlytothetransmissiou facilities and connect a recorded message-to the locallistenerson the excess lines.

The output of AND gate 131 enables'OR gate 138'to apply asignal to ORgate k124 in timing vand repeater circuit 162. The output of OR gate 124resets bistable device 114 and continues to inhibit thetiming of thenew... a

annabee The transmission of switch-out'signals is thereby disabled oncea verification switch-out signal is received.

VFrom the above description, it is,Y apparent that the switchingsystem'of the present invention contemplates the use of coded switchingsignals transmitted back and forth between a localand a remote terminal.The switchout signal, which can be originated at either terminal, is

Immediately uponl ff Becausel the period Yfor which the remote vterminalwaits,l

as determined by delay circuit 132, is exactlyequal to amplifier 109',Aused to seizethe signaling channel 111, also utilized to operate aslow-to-operate relayf139. The operate time of relay 129 is 'chosen suchthat-timing and repeater circuit 102 has an opportunity to repeat theswitch-out signal several times', for example, tive times. second,armature 140 on relay i139 closes on contact 141 and connects battery142 tolead 143.' V The battery voltage'on lead 143 serves to enableORgate.-138 and apply a signal to OR gate124. vWhen thus enabled, ORgate `124 produces an output which resets bistable device After thisinterval, in i'theifexample one-half l put on lead'129.

114 and maintains bistable device 114 in this condition as long as relay139 remains operated. The signal on lead 143 thus serves to inhibit anyfurther repetition of the switch-out signal after live trys.

three-input AND v gate 144. Another input to ANDV .been received to setbistable device 128. When ANDy gate 144 is fully enabled, it produces anoutputl which is applied to amplifier 146. 'Ihe output of amplifier 146may be used to operate any suitable audible or visual alarm. The`operation of such an alarm indicates to attendant personnel that aswitch-out operation has been locally initiated and has not beencompleted due to someV failure in the switch-out signaling. The outputof amplifier 146 is used to automatically eiect local switch-v out or,if it is preferred, the attendant personnel may.

manually connect a battery to switch-out bus 136 to The output on lead143 is also applied to one input of 10 out signal; Signaling channel 111"has been seized by the operatian of relay 110 inthe vsame manner as forvswitch-out. Y y

At the rerriote terminal, the switch-in signal is receivedby'signaling"receiverV y12.6 and produces an output on lead 127' to "setbistable device 128. The output of bistable device 128', which appearson lead 129', is applied to AND gate 130', and gate 131 and delaycircuit equal to the propagation'time of the transmission facility andserves to place a signal on switch-in bus 137 by way of OR gateff134'and-'amplifier 135. vAs mentioned earlier, the signal on switch-in bus137 serves to disablev the holding circuits in"y the primary and excessline switches of the remote terminal andreturn the TASI facilitiestoservice." l Y The output onY lead 129 also serves to Acomplete theenablement o f AND gate 130' and, by way of OR gates 106', 107'and=108,'lto' initiate the transmission of verifcation switch-insignals. In performing this function, timing and repeater circuit 102operates in the same manne-r asin the switch-out operation.

Upon receipt ofwthe verification switch-in signal by signaling receiver126 at the local terminal; bistable device y128' is set by 'way'of lead127 and produces an out- This .output on lead 129 completes theenablementI-of AND gatet131 and produces a signal on switch-in bus'137by Way 'of OR gate 134' and amplilier 135. Again, if all Signals aretransmitted and received, the' two terminals will switch-insimultaneausly yto provide uninterrupted ser-vice on the primary lines.

It will be noted that an alarm has not been provided to indicate thatthe switch-invoperationwhich has been initiated has-not beensuccessfully completed. While such anv arrangement could easily beprovided, the

arrangements of the present invention contemplate that personnel'willalready be in immediate attendance and will notfhave'to be told by an'valarm of a failure. A switch-inrzlamp-'147 is provided, however, to tellthem ywhen the. switch-in operationjis completed. Lamp 147 is connectedto switch-in bus 137 and will light when this bus is energized by asuccessful completion of a completeround.-` trip bythe switch-insignals.

Itwill be noted that leads 148 and 148 have been Y provided to 'resetswitch-out and switch-in logic circuits 101 and 100, respectively. Asignal applied to. either of these leads resetsthe associated bistabledevice (104 or 104') and prepares these circuits fora future switchingoperation. A'signal on reset lead 14S also resets bistable device 128`andl 128 to prepare these devices for future switching operations. Y

A switching system has been described for simultaneously switching localand remote terminals to remove effect the local switch-out. i Remoteswitch-out must then be accomplished separately as soon as the attendantpersonnel at the remote terminal can be made aware of the failure. Y i li The'switch-in operation is carried out in almost an identical manneras the switch-outoperation. A switch- 4in signal manually orautomatically applied to lead 150 serves to set bistable device104f and,produce an outputon lead 105. The output'on lead 105 is applied toORgate 108 to initiate Vthe'timing operation in timing Y and repeatercircuit 102 and to partially enable AND gate 107. AND gate 107 iscompletely enabledby the output of timing and repeater circuit 102 onlead 115 for ten out Vof every hundred milliseconds and thusv energizeslead116 for the correspondingperiods. Lead 116', however, controlssignaling transmitter 117 so as'f' to transmit a coded switch-insignalrather than a switchspecific equipment from. service;

While the switching system ofthe present invention has been describedwith reference to time assignment speech interpolation facilities, it"is to be understood that these arrangements are only illustrative ofnumerous and Avaried other arrangements which could representapplications of the principles of the invention. Such other arrangementsmay readily` be devised by those skilled in the art without departingtion means, switching control means for connecting said i saidcommunication vsystemto a second terminal of said fis A communicationsystem, means responsive to the reception of said switching signal fortransmitting a verifica- Delaylcircuit 132" 'alsoV provides a delaytime' v@animee tion signal from said second terminal to saidrst,.`terminal, means at said first terminal, responsive-to thereception of said verification signal, for connecting saidV transmissionchannels directly tolselected ones of said 3. The combination accordingto `claim l further. in-l cluding means for repeatingrthe transmissionof said switching signalefrom said first terminal to said second Yterminal at regular intervals and meansfor disabling said repeatingmeans in response to the reception of saidv veriiication signal.

4. The combination according to claim 3 further ini cluding means foroperating said disabling means after a iixedV interval'of time.regardlessv of the reception ofV` said verication signal, and meansresponsive to said operating means for generating an alarm signal.

5. in a transmission system having two geographically separated terminalstations, and a plurality of trans-Y mission lines extendingr betweensaid terminal. stations, means for simultaneously switching saidtransmission lines at both of said terminal stations,which switchingIneensv comprises means for transmitting a switching signal from one ofsaid terminal stationsrto the other of said terminal stations, means fordetecting said switchingl signall simultaneously switching saidtransmission ch nnels at said one terminal station. e y 6. `Iny atwo-way transmission system including terminal stations and a pluralityof signal transmission lines for each direction of transmissionextending between said terminal stations, means for initiatingasupervisory op#V eration at one of said terminal stations, means fortransmitting a supervisory signal indicative of said operation over oneof said signal transmission rvlines to the other o said terminalstations, means responsive to the reception of said supervisory signalfor transmitting. a verification signal to said one terminal station,means also responsive lto the reception of said supervisory signal butafter a delay equal to the propagation time of said transmission systemforperfrorming said supervisory opera-- tion at said other `terminalstation, andmeans responsive to the reception of said verificationsignal for simultane? ously performing saidsupervisory operation.- atsaid one terminal station. Y Y

7. kin a communication. system utilizing time assignment facilities forconnecting individual ones'of a plu'- r'ality of signal sources toindividual ones of alesser plurality of transmission lines only when theindividualsignal source is active and the individual transmission lineis idle, and for connecting saidrtransmission lines to utilization meanscorresponding to saidsignal sources, means for utilizing saidtransmission lines during. failure of'. said: time assignment facilitieswhich comprises means responsive to the failure of said time assignmentfacilities for'transmitting a switch-out signal in one. direction alongone of said transmission lines, means for transmitting a ve'ricationsignal in the other directionalong saidV oney transmission line, meansresponsive to said switch-out and vericationjsignals for simultaneouslyconnecting said transmission lines to selected ones of said signalsourcesequal in number to said lesser'plurality and. simultane# ously tothecorresponding onesof saild utilization means.

Reerencesi'Cited in the file of this patent Albrighton et al. ...n Aug.6, 1957

